1. Field of the Invention
The present invention relates generally to improvements in optical correlator systems and more particularly, pertains to a new and improved optical correlator structure to provide enhanced optical detection of an unknown object.
2. Description of Related Art
Many applications including military, medical and security have a requirement for small, lower power, low cost pattern recognition systems that are capable of locating and identifying targets or anomalies. Optical correlators can perform two dimensional pattern recognition at much greater rates than digital systems of comparable size, power and/or weight.
Many modem real time pattern recognition or pattern analysis problems, both military and commercial, can be resolved through the use of correlation. Military missions require a real-time pattern recognition capability for target detection, target recognition, munitions guidance, and many other applications. Commercial applications require a pattern analysis capability for many medical, intelligence, law enforcement, security, robotics and factory inspection applications. Specifically, there is a demand for an optical correlator pattern recognition system that is rugged, low cost, has a lower power configuration, and is very compact, temperature stable and light weight. The processing requirements for robust pattern recognition at real-time rates is very high. Current and near-term digital solutions are still not practical for many applications with respect to the cost, size, weight and power requirements.
The reflective optical correlator with a folded asymmetrical axis of U.S. Pat. No. 5,311,359 assigned to the same assignee as in the present application, discloses an optical correlator pattern recognition system that provides the processing power required at real-time rates in a small, low weight, lower power package.
FIG. 1 is an illustration of the reflective optical correlator system of U.S. Pat. No. 5,311,359. The optical correlator system 10 has a planar support body 12 with an irregular perimeter 14 and a plurality of system stations 16, 18, and 24 formed at selected locations along the irregular perimeter of the support body. A plurality of reflective optical components, which are both active 16 and passive 18, are positioned at the selected system stations. An electromagnetic radiation source 20 is positioned at a first system station. Radiation source 20, for example, may generate a coherent light beam, which traverses a folded asymmetrical optical axis or path 22 within the planar body 12, as bounded or defined by the reflective optical components 16 and 18. The optical path 22 terminates at a detector 24 positioned at the last system station.
FIG. 2 is an illustration of an optical correlator system within which the optical correlator 10 of FIG. 1 could be utilized. A specific preferred structure for the optical correlator 10 is disclosed in U.S. Pat. No. 5,311,359. The entire disclosure of U.S. Pat. No. 5,311,359 is incorporated herein by reference.
The basic concept of operation of an optical correlator 10 is illustrated by the system diagram of FIG. 2. Images 46 to be processed by the optical correlator system may be sensed by an input sensor 44, which may be an external digital camera, or any other source of image/signal data to be processed. The sensed data is provided to an image pre-processor, data formatter 42 which takes the data from the input sensor 44 and formats it for the input drive electronics 34 of a spatial light modulator (SLM) 28. SLM 28 is illuminated by a coherent beam of light from the radiation source 20, which may be a laser diode. The data supplied to the SLM 28 by the input electronics 34 patterns the light beam from the laser 20 which has been passed through a polarizer lens 24. SLM 28 reflects the patterned light beam to a first concave mirror 26 which reflects the received patterned information through a first polarizer 27 to a second spatial light modulator (SLM) 30 as a patterned Fourier transform beam. This second SLM 30 also receives filter data from filter storage in filter drive electronics 36 that represents anticipated images, as directed by a post-processor 40. This filter data is in the form of a preprocessed Fourier transformation pattern. The second SLM 30 receives the patterned Fourier transform beam at the same time as it is patterned with the Fourier transformation pattern of a known filter from the filter data base 36. This causes a multiplication of the two Fourier patterns where matches occur, and zeros where they do not match. The combined pattern of the second SLM 30 is reflected to a second concave mirror 29. The second concave mirror 29 reflects and focuses a Fourier transform of the combined pattern of SLM 30 through a second polarizer 31 onto a high speed photo detector array, such as a CCD array. The patterned beam CCD detector array 32 captures the resultant image. Detector electronics 38 and post-processor 40 use the detected information to generate an output 48 that displays the position of the original input image 46 as determined by the filter image from the data base. The amplitude of the display indicates the extent of the correlation.
For a more detailed example and explanation of an optical correlator system and structure using spatial light modulators and Fourier transform lenses, reference should be made to U.S. Pat. No. 5,418,380.
The present invention provides an improved folded and segmented optical image processor over these prior art systems.